1. Field of the Invention
The present invention relates to a color image display apparatus which restores original color image from compressed color image containing compressed color information.
2. Description of the Prior Art
FIG. 1 is the schematic block diagram of a conventional digital color image display apparatus. A memory means composed of floppy-disc system or optical-disc system for example stores a plurality of color image information. A memory means 1 stores compressed color image information containing color information compressed by color-compressing means described later on.
A graphic processor 2 reads compressed color image information from the memory means 1, and then, transfers the compressed image data to the frame memory 3. Simultaneously, the graphic processor 2 sets palette data as the information for restoring color in the color palette 4.
A frame memory 3 stores image data read out by the graphic processor 2 from the memory means 1 per one frame on the screen of a CRT display unit 8.
A color palette 4 restores original color image data from image data before delivering it to the CRT display unit 8, with means by palette data delivered from the graphic processor 2 and stored in frame memory 3 in accordance with information for restoring original color image from compressed color image.
By applying digital signals, any conventional digital color image display apparatus having the constitution mentioned above designates color containing picture elements needed for display, more particularly, it designates applicable colors by individually specifying luminance of threeprimary color components of light including red (R), green (G), and blue (B). On the other hand, the more the number of expressible colors, the more is the needed number of bits of digital signals designating colors. For example, to fully express 4,096 colors, a total of 12 bits (4 bits for each three-primary color components) of color information is needed for each picture element.
To compensate for this, conventionally, a technique for reducing the amount of data by compressing color information of color image is employed. For example, this technique first selects 256 units of three-primary color data mostly used for each picture, and then sets these data to color palette 4 so that these can function as palette data when displaying image. This allows color information to be expressed using 8 bits, thus effectively reducing 4-bit data from each picture element.
Normally, any conventional color image display apparatus causes the memory means 1 to store each unit of image information of a frame image by combining the image data with the palette data which is needed for restoring original color from image when displaying color image.
When displaying color image, the graphic processor 2 reads out image information from the memory means 1. Of the read-out image information, the palette data is delivered to the color palette 4 and image data to the frame memory 3, and both data are provisionally stored in the color palette 4 and the frame memory 3, respectively. The color palette 4 restores original color from image data in the frame memory 3, which are shown on the screen of the CRT display unit 8.
Because of the constitution mentioned above, any conventional color image display apparatus needs to deliver each palette data to the color palette 4 and then restores the original image color before eventually displaying each color image. Consequently, when compositing those images containing a variety of the palette data into a single image, any conventional color image display apparatus cannot restore colors of those image data composited by the frame memory by applying identical palette data. To compensate for this, any remedy means using software should be applied. However, actually, it takes a long period of time before implementing remedy means.